Glow discharge tube and circuit therefor



g- 7, 1956 E. c. LUSK EFAL 2,758,253

GLOW DISCHARGE TUBE AND CIRCUIT THEREFOR Filed Sept. 14, 1953 J REULATED OUTPUT VOLTAGE 22 uvvmvrms, UNREGULATED ELMEI? c. LUSK,

gtgff JAMES E. DREW/VAN,

FRANCIS CZ TODD.

A 7' TORNE X GLOW DISCHARGE TUBE AND CIRCUIT THEREFOR Elmer C. Lusk and James E. Drennan, Columbus, and Francis C. Todd, Amlin, Ohio, assignors to the United States of America as represented by the Secretary of the Army Application September 14, 1953, Serial No. 380,149.

15 Claims. (Cl. 3'15339) This invention relates to voltage regulators and more particularly to regulators of the gaseous glow discharge type.

In prior voltage regulator devices utilizing glow discharge tubes of the cold cathode type, operation at high currents results in oscillations in the output due to the very irre ular voltage-current characteristics of the tubes.

Reference is made to the copending application of Francis C. Todd et 211., Serial No. 258,934, filed November 29, 1951, in which a so-called hollow cathode type of gaseous voltage regulator tube is disclosed and claimed. Such tubes have been operated successfully at currents as high as 890 milliamperes, but the best results are produced when operated over a current range of to 460 milliamperes. When such tubes are operated in the upper region of this current range, oscillations with amplitudes as high as 20 volts peak appear in the output voltage which are similar to the oscillations which appear when conventional glow discharge tubes are operated at higher currents.

One of the objects of this invention is to provide a novel gaseous glow discharge device and circuit therefor having improved characteristics for reducing oscillations in the regulated output voltage.

Another object of this invention is to provide an improved hollow cathode voltage regulator tube having improved voltage regulating characteristics.

In accordance with this invention, a gaseous glow discharge device of the hollow cathode-type is provided with one or more screen grids between the anode and cathode, the screen being coarse enough to permit the glow to extend through to the anode. This serves to reduce the anode space charge.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, in which:

Fig. l is a plan view, taken in section along B-B of Fig. 2, of a gaseous discharge tube built in accordance with the invention;

Fig. 2 is an elevational view taken in section along A-A of Fig. l; and

Fig. 3 is a schematic diagram of a novel voltage regulator circuit incorporating the gaseous discharge tube illustrated in Figs. 1 and 2.

The hollow cathode referred to in this application is a type of cathode capable of maintaining a so-called hollow cathode glow. In order to produce a hollow cathode glow, it is necessary to have in the envelope of a glow discharge tube two or more cathode elements spaced not more than two cathode dark spaces from each other; otherwise the hollow cathode glow will not form. Such a hollow cathode glow is produced by the interaction of two cathode glows, in the interspace between the cathode elements and not merely between the anode and the cathode element.

The hollow cathode glow is to be distinguished from the anode glow, which exists between the anode and the I 2,758,253 Patented Aug. 7, 1956 edges of the cathode elements, whereas the hollow cathode glow exists in the interspace between the cathode elements. For example, in a tube using a double cathode, the discharge strikes from the anode to the spaced edges of the cathode elements. A very intense illumination appears between the spaced cathode elements and, at the upper end of the current range, this new illumination extends between the spaced cathode elements from their top to bottom. and outwardly toward the sides. In addition to the new illumination which appears between the spaced cathode elements, the anode blow, which is due to the anode fall of potential, is also present. The spaced cathode elements usually have a field-free space therebetween, which constitutes the interspace referred to above. The extent of the interspace is determined by the pressure of the filling gas.

It has been found that oscillations are associated with the anode glow. The conditions for the appearance of the anode glow are well known and have been widely discussed in the literature. According to the generally accepted theory of Langmuir and Mott-Smith, which appeared in General Electric Review 27, 762 (1924), a positive anode fall develops when 1 jrF i (1) where i is the anode current, F is the surface area of the anode which is in the Faraday. dark space or glow, and, in its position, ii is the density of the randomelectric current. With assumptions of temperature equilibrium and in the absence of space charge, kinetic theory predicts the following relation between the current density of electrons and the density of ionization:

jr=%nev (2) When n is the number of ion pairs per cubic centimeter, e is the electron charge, and v is the average velocity. Thus, a positive anode fall develops when:

i AneF F 3) The anode glow appears when the anode fall of potential has increased until it approaches the ionization or resonant potential of the gas.

From Equation 3, it can be seen that the anode fall of potential can be eliminated by making the right-hand side of Equation 3 as large as possible. The anode fall of potential cannot appear when the right-hand side of Equation 3 exceeds the total tube current. In accordance with this invention, this is accomplished by the insertion of one or more mesh screens between the anode and the cathode and controlling the current to each screen. The use of screens between the anode and cathode results in an increase of the effective area of the anode. The spacing between the wires forming the screens and the potentials applied thereto must be such as to permit sufiicient discharge to how to the anode.

Referring now to Figs. 1 and 2, there is shown a volt age regulator tube 10 composed of an anode 18, wire mesh screens 20 and 22, and a hollow cathode composed of a pair of cathode elements 12 and 14, all enclosed in a sealed envelope 16. Although all these elements are shown as concentrically disposed cylinders, it is to be understood that the invention is not restricted to such construction. Cathode elements 12 and 14 may be connected together internally or externally so as to maintain them at the same potential. The tube leads to the various elements and their supports have been omitted for the purpose of clarity. The envelope 16 is filled with an attenuated gaseous atmosphere suitable for maintaining a glow discharge. This atmosphere may include one or more of the following gases: hydrogen, nitrogen, helium, neon, argon, krypton, xenon, mercury vapor and sodium vapor.

The constructional details of the tube elements depend, of course, on the desired characteristics. In onetube built, the details are as follows: anode 18 may be made of nickel, and is shaped in the form of a solid cylinder having a diameter of approximately Screens 20 and 22 may be made of nickel or tungsten. These screens surround the anode for a portion of its length. The first screen 20 is spaced approximately ,5 from the anode and has a diameter of /z", and encloses as much of the anode as possible. The second screen 22 isspaced approximately from the first screen and has a diameter of /8" and totally encloses screen 20. Cathode elements 12 and 14 are preferably made of molybdenum or tungsten, although other metals are suitable. Cathode element 14 is 1%" in diameter, and is spaced /2" from anode 18. The space between cathode elements 12 and 14 is .020" to .060", the exact spacing being dependent upon the gas pressure which, as above pointed out, determines the extent of the dark space. The screens consist of a grid made up of 0.032" x 0.125" nickel strips with 0.125" spacing therebetween.

The circuit shown in Fig; 3 employs the novel voltage regulator tube with an unregulated voltage supply 24 to produce a regulated output voltage at 26. The anode 18 is connected to the positive terminal ofthe. voltage supply 26 through resistor 28 and cathode elements 12 and 14 of the hollow-cathode are connected to the negative terminal of the voltage. supply. The screens 20 and 22 are connected respectively through resistors 30. and 32 through resistor 28 to the positive terminal. The current to the anode and the screens is controlled by the size of resistors 30 and 32. Variations of these resistors will vary the anode current. The regulated output voltage at 26is taken across anode 18 and the common junction of cathode elements 12 and 14, and will be free of any large voltage oscillations.

This invention is not limited to hollow cathode voltage regulator tubes but can also be used with conventional cathode voltage regulator tubes where high output currents are desired.

Since many widely different embodiments of the invention may be made Without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments disclosed.

What is claimed is:

1. A glow discharge tube comprising a sealed envelope having therein an attenuated gaseous atmosphere and at leastan anode and a pair of spaced, electrically connected cathode electrodes, said cathode electrodes having a spacing therebetween substantially throughout their extents which is not more than twice the extent of the cathode dark space at each cathode electrode, and at least one auxiliary electrode between said cathode'and anode and connected to said anode to substantially eliminate the anode fall of potential.

2. A glow discharge tube as set forth in claim 1, wherein said cathode electrodes at least partially surround said anode.

3. A glow discharge tube as set forth in claim 2, wherein said anode is cylindrical and said cathode electrodes are cylindrical and concentric with said anode.

4. A glow discharge tube as set forth in claim- 3, wherein said auxiliary electrode is a cylindrical grid concentric with said cathode and anode.

5. A glow discharge tube as set forth in claim 4, wherein said grid substantially entirely encloses said nod 6. In combination with a source of D. C. potential, a circuit for improving the regulation of said source comprising a glow discharge tube comprising a sealed envelope filled with an attenuated gaseous atmosphere and atleast an anode electrode connected to the positive terminal of said source a pair of cathode electrodes connected to the negative terminal of said source, and a pair of output terminals respectively connected to said anode and cathode; said cathode electrodes being near enough to each other that their cathode glows are at least contiguous substantially throughout their extents, whereby their interaction causes an intense glow to form in the space between said electrodes.

7. A circuit as set forth in claim 6, wherein said anode and cathode electrodes are cylindrical and concentric, said anode being surrounded by said cathode electrode.

8. A circuit as set forth in claim 6, including means to reduce. the anode fall of potential, said means comprising at least one grid situated between said anode and cathode, and a connection including a resistor connecting said anode electrode and said grid.

9. A circuit as set forth in claim 8, including a resistor connected between oneof said electrodes and said source.

10. A circuit as set forth in claim 9, including means connecting said cathode electrodes together to maintain them at the same potential.

11. A circuit as set forth in claim 6, including means to maintain said cathode electrodes at the same potential.

12. A circuit as set forth in claim 6, including a resistor connected between one of said electrodes and said source.

13. A circuit as set forth in claim 6, including a resistor connected between the anode and said source.

14. In combination with a source of D. C. voltage, a voltage regulating means therefor comprising a glow discharge tube having an envelope containing an attenuated gaseous atmosphere, an anode electrode surrounded by a pair of spaced cylindrical cathode electrodes, the spacing between said electrodes, substantially throughout their extents, being such that their cathode glows are at least contiguous whereby an intense glow tends to form in the space between said cathodes, means to substantially eliminate the anode fall of potential comprising a pair ofspaced, cylindrical grids concentric with, and substantially enclosing said anode and situated between said anode and cathode electrodes, said anode being connected in series with a resistor to the positive terminal of said source, said cathodes being connected to the negative terminal'of said source, resistive circuits connecting said grids to said anode, and a pair of output terminals respectively connected to said anode and to said cathode electrodes.

15. In combination with a source of direct-current potential, a glow-discharge tube circuit for improving the regulation of said source, said glow-discharge tube comprising an envelope having therein an attenuated gaseous atmosphere, a cylindrical anode, a cathode and means located between said anode and cathode for reducing the anode fall of potential, said means comprising at least one cylindrical mesh grid which is concentric with said anode and which is at least coextensive with said anode and cathode, a connection including a first resistor in series between said anode and the positive terminal of said source, a connection between said cathode and the negative terminal ofsaid source, a connection including a second resistor between said grid and the junction of said anode and said first resistor, and output leads for said circuit connected to said anode and cathode.

References Cited in thefile of this patent UNITED STATES PATENTS 1,861,453 Sashoff June 7, 1932 2,184,756 Rockwood Dec. 26, 1939 2,466,749 Stutsman e Apr. 12, 1949 

